Automated thermal cyclers for performing PCR simultaneously on a number of samples are disclosed in U.S. Pat. No. 5,038,852. Briefly, PCR is an enzymatic process by which a small amount of specific DNA sequences can be greatly amplified in a relatively short period of time. The method utilizes two oligonucleotide primers that hybridize to opposite strands and flank the region of interest in the target DNA. A repetitive series of thermal cycles involving template denaturation, primer annealing, and the extension of the annealed primers by DNA polymerase results in the exponential accumulation of a specific DNA fragment whose termini are defined by the 5' ends of the primers.
A reaction mixture made up of the target DNA to be amplified, oligonucleotide primers, buffers, nucleotide triphosphates, and preferably a thermostable enzyme such as Taq polymerase, are combined and placed in reaction tubes. The reaction mixture contained in the tubes is then subjected to a number of thermal transition and soak periods known as PCR protocols in a thermal cycler to generate the amplified target DNA.
An array of reaction tubes is typically made up of up to either twenty four or forty eight or ninety six tubes arranged in a 8.times.3 array or a 6.times.8 array or an 8.times.12 array in a tray. The array of tubes is placed in a metal thermal cycler block so that the lower portion of each tube is in intimate thermal contact with the block.
The temperature of the block is then varied in accordance with the predetermined temperature/time profile of the PCR protocol for a predetermined number of cycles.
Holder assemblies for reaction tubes are preferably compatible with microtiter plate format lab equipment while maintaining sufficient individual tube freedom of movement to compensate for differences in the various rates of thermal expansion of the various components.